Shores and Islands 67 
the land by rivers, and the remains of marine animals and 
plants are deposited by wave action on certain shores with 
the result that instead of wearing away they are growing 
larger. There is often a gradation of size in the particles form- 
ing such a beach from coarse particles above the waterline to 
very fine sand and mud below it. Examples of deposition are 
the coastal plain of Texas and the shallow reef-bordered 
sounds of North Carolina. Another beach building process 
is the rising of the land. 
OCEAN ISLANDS 
Two kinds of ocean islands should be distinguished: the 
island which rests upon a continental shelf, which is merely 
a projecting part of the continent, and the true oceanic is- 
land. The true oceanic island reaches to the surface from the 
depths of the ocean, and may be either volcanic or coral in 
nature. Charles Darwin, at the age of 25 years, conceived of 
the following explanation for coral islands. The original is- 
land is supposed to have been volcanic in nature. In the 
course of many years it began to sink back into the ocean, 
but a ring of coral growing on its shores gradually built up 
into a ring around it until finally when the volcanic part of 
the island had completely sunk from view the coral ring was 
all that was left, forming an atoll with enclosed lagoon. 
CONTINENTS MOVING? 
While we are on the subject of shores it may be interest- 
ing to say a few words about Wegener's theory of conti- 
nental drift. According to Wegener, grand “old man” of geo- 
physics, all the land of the world was once gathered together 
in one huge continent called the world island. Due to some 
rather mysterious forces the island broke up into the con- 
